Why every 20 min or so does my ipad say wrong wi-fi password,when i have not even entered it.

Are you connected to your home WiFi network, or are you in a hotspot - say at Starbucks or somewhere like that? Sometimes the iPad attempts to join to another WiFi network and, if that network has been joined previously (i.e. it's a 'known network') then it will do this without prompting you and will attempt to use the password that it last used for that network. If the owner/operator of that network has changed the password, then you will get the 'wrong password' message from the iPad as it attempts to join that network using the old password that it has stored.

Tim